(1) Field of the Invention
The present invention relates to the generation of coherent light and, particularly, to excitation field shaping improvements in lasing devices characterized by a uniquely configured discharge cavity in which a stable plasma is area cooled by non-conductive sidewalls which also perform a light guiding function. More specifically, this invention is directed to improvements to RF excited gas lasers, and especially to lasers characterized by a discharge region having a generally curvilinear orthogonal cross-section, the shorter dimension of the discharge region being defined by the spacing between a pair of non-conductive sidewalls which are suitable for guiding laser light and which collisionally cool the discharge. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
The present applicant has invented an RF excited gas laser having a discharge region cross-section of unique configuration. This invention is disclosed in the above-referenced related application which is incorporated herein by reference. Devices disclosed in the related application are known in the art as area cooled "slice" lasers for the purpose of distinguishing such devices from previously known area cooled "slab" lasers. A "slice" laser is characterized by an elongated gaseous discharge chamber or cavity which, for purposes of explanation, may be considered to have a generally rectangular cross-section. The discharge cavity cross-section is in part defined by a pair of non-conductive spacers which form opposed sidewalls. The average shorter dimension W of the discharge region cross-section is measured between these sidewalls. An excitation field(s) established in the cavity bounded by these sidewalls and another pair of oppositely disposed walls which interconnect the sidewalls will create a plasma discharge in a lasing gas confined in the discharge cavity. The other pair of discharge cavity defining walls, solely for purposes of explanation, may be considered to be the field establishing electrodes. The longer dimension D of the discharge region cross-section is thus the average spacing between electrodes of opposite polarity. Consequently, a slice laser has a discharge region cross-sectional shape where D/W&gt;&gt;1. Prior art D/W&lt;&lt;1 "slab" lasers were characterized by a discharge chamber defined in part by closely spaced parallel electrodes, i.e., electrodes having a width which was much greater than the electrode separation, and it was believed that an "input of 10-50 W/cm.sup.2 " was "possible only with a self-sustaining transverse RF discharge in a chamber with a small interelectrode spacing". Thus, prior to the invention of the related application, it was not thought possible to create a stable area cooled D/W&gt;&gt;1 discharge in a device having the above-described slice characteristics (Ref. Y. P. Raizer, M. N. Shneider and N. A. Yatsenko, "Radio-Frequency Capacitive Discharges", copyright CRC Press 1995, ISBN 0-8493-8644-6.